1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor and a method of preparing the photoreceptor, and to an image forming method, an image forming apparatus and a process cartridge therefor using the photoreceptor.
2. Discussion of the Background
Recently, organic photoreceptors (OPCs) have been widely used instead of inorganic photoreceptors for copiers, facsimiles, laser printers and their complex machines because of their good performances and advantages. Specific examples of the reasons include (1) optical properties such as a wide range of light absorbing wavelength and a large amount of absorbing light; (2) electrical properties such as high sensitivity and stable chargeability; (3) choice of the materials; (4) good manufacturability; (5) low cost; (6) non-toxicity, etc.
On the other hand, as image forming apparatuses become smaller, photoreceptors have smaller diameters recently. In addition, photoreceptors are required to have high durability as image forming apparatuses produce images at a higher speed and are free from maintenance. In this respect, the organic photoreceptor typically has a soft surface layer mainly formed from a low-molecular-weight charge transport material and an inactive polymer, and therefore the organic photoreceptor typically has a drawback of being mechanically abraded with an image developer and a cleaner with ease when repeated used in the electrophotographic process. In addition, as toner particles has smaller particle diameters due to requirements for high-quality images, cleaning blades need to have higher rubber hardness and higher contact pressure for the purpose of increasing cleanability, and which also accelerates abrading photoreceptors. Such abrasions of photoreceptors deteriorate electrical properties thereof such as sensitivities and chargeabilities, and cause abnormal images such as image density deterioration and background fouling. When a photoreceptor is locally abraded, images having black stripes due to defective cleaning are produced. At present, photoreceptors are exchanged because of these abrasions and damages.
Therefore, it is indispensable to decrease the abrasion amount of the organic photoreceptor so as to have high durability, and which is the most pressing issue to solve in this field.
As methods of improving the abrasion resistance of a photoreceptor, (1) Japanese Laid-Open Patent Publication No. 56-48637 discloses a photoreceptor using a hardening binder in its surface layer; (2) Japanese Laid-Open Patent Publication No. 64-1728 discloses a photoreceptor using charge transport polymer material; and (3) Japanese Laid-Open Patent Publication No. 4-281461 discloses a photoreceptor having a surface layer wherein an inorganic filler is dispersed.
To improve the abrasion resistance of the photoreceptor of (1), Japanese Patent No. 3262488 discloses a photoreceptor including a hardened acrylate monomer.
As an abrasion resistance technology of a photosensitive layer in place of these technologies, Japanese Patent No. 3194392 discloses a method of forming a charge transport layer using a coating liquid formed from a monomer having a carbon-carbon double bond, a charge transport material having a carbon-carbon double bond and a binder resin. The binder resin includes a binder resin having a carbon-carbon double bond and a reactivity with the charge transport material, and a binder resin having neither a carbon-carbon double bond nor a reactivity with the charge transport material.
Japanese Laid-Open Patent Publication No. 2000-66425 discloses a photosensitive layer including a hardened positive hole transport compound having two or more chain polymerizing functional groups in the same molecule.
Taking these inventions into consideration, the present inventors discovered that a surface layer formed of a crosslinked resin, wherein at least a radical polymerizing monomer having three or more functional groups not having charge transportable structure and a radical polymerizing compound having charge transportable structure are hardened, improved electrical properties and abrasion resistance of the resultant photoreceptor. However, it cannot be said that this surface layer formed of a crosslinked resin has sufficient durability, and the surfaceness largely varies depending on the crosslinking conditions, i.e., the surface concavities and convexities tend to be large. Therefore, the surface of a photoreceptor is so poorly cleaned that a cleaning blade therefor is locally chipped, resulting in abnormal striped images.
Because of these reasons, a need exists for a long-life and high-performance electrophotographic photoreceptor having high abrasion and scratch resistance, good electrical properties, and producing high-quality images for long periods.